1. Field of the Invention
The present invention relates to a thermal head, a printer, and a manufacturing method for a thermal head.
2. Description of the Related Art
There have been conventionally known a thermal head which is used in a thermal printer often installed to a portable information equipment terminal typified by a compact hand-held terminal, and which is used to perform printing on a thermal recording medium based on printing data with the aid of selective driving of a plurality of heating elements (for example, see JP 6-166197 A).
In terms of an increase in efficiency of the thermal head, there is a method of forming a heat insulating layer below a heating portion of a heating resistor. By formation of the heat insulating layer below the heating portion, of an amount of heat generated in the heating resistor, an amount of upper-transferred heat which is transferred to an abrasion resistance layer formed above the heating portion becomes larger than an amount of lower-transferred heat which is transferred to a heat storage layer formed below the heating portion, and hence energy efficiency required during printing can be sufficiently obtained. In the thermal head described in JP 6-166197 A, a hollow portion is provided below the heating portion of the heating resistor, and this hollow portion functions as a hollow heat insulating layer. Thus, the amount of upper-transferred heat becomes larger than the amount of lower-transferred heat, and the energy efficiency is increased.
Further, in a printer in which a thermal head is installed, thermal paper is pressed, with a predetermined pressing force, against a head portion of a surface of the abrasion resistance layer formed above the heating portion by a platen roller. Therefore, the thermal head is required to have heating efficiency for improving printing quality as described above, and required to have strength for withstanding the pressing force of the platen roller.
However, in the conventional thermal head, in order to increase heat insulating performance of a substrate, the hollow portion is enlarged, and the thickness of the heat storage layer between the heating resistor and the hollow portion is thinned. As a result, when external load is applied to the heating resistor, excessive deflection occurs in the heat storage layer. Then, when tensile stress due to the deflection becomes larger than breaking stress of glass, there arises a problem that the heat storage layer breaks. Further, when large deflection occurs in the heat storage layer by the pressing force of the platen roller, a contact state between the thermal paper and the head portion is deteriorated, and contact pressure is reduced, whereby there arises a problem that it becomes difficult to transfer heat to the thermal paper.